U.S. Pat. No. 3,718,439 discloses a photometric instrument of a type in common use for performing clinical chemical diagnostic analyses. The patent also shows and describes a three-chambered plastic cuvette for use in such an instrument, the cuvette including a pair of planar side walls, two end walls, and two partitions or barrier walls which divide the interior of the cuvette into three separate compartments. The result is a rigid cuvette structure which may be readily inserted into the instrument for the performance and recording of any of a variety of diagnostic tests. For example, where the test is one which utilizes a standard mode, such as a serum glucose test, all three compartments of the cuvette would contain a liquid reagent. As is well known, a laboratory technician would add measured amounts of a serum standard and a patient's serum, respectively, to two of the compartments, the third compartment having nother further added to it and serving merely as a blank. Optical density of the solution in each chamber is then measured automatically by projecting a beam of light therethrough and comparing the intensity of the transmitted light to the incident light, such optical density being representative of the concentration of the solution.
Measurement precision requires that the light impinging on the detector consist of light transmitted through the solution, in contrast to light which might reach the detector by any other route. If the material of the cuvette serves as a light pipe, then it is believed apparent that the accuracy of the test results may be adversely affected because of light reaching the detector via a route other than through the solution being tested. Thus, should light be piped from the chamber undergoing examination into an adjacent chamber, at least a fraction of that diverted light may be scattered by the contents of the adjacent chamber back into the original chamber, or possibly even directly to the detector, to adversely affect the test results. The detector would necessarily be sensing the light transmission characteristics of the contents of more than one chamber at the same time; even in the unlikely event that the contents of the successive chambers were the same, the readings would lack uniformity because a test on the contents of the middle chamber would be affected by scattered light from both end chambers whereas a test involving an end chamber would be affected by scattered light from only one side.
Such undesirable light piping effects might be reduced by treating the internal surfaces of a cuvette so that light striking the barrier walls between chambers would be blocked from entering and returning from adjacent chambers and, in actual practice, the walls (particularly the "barrier" walls) of commercial versions of the cuvette disclosed in U.S. Pat. No. 3,718,439 are etched or frosted to reduce objectionable light transmission through the walls so treated. A major disadvantage of such treatment is that it is a relatively expensive procedure in the production of a product intended for use as a disposable item. While a lower cost solution to the problem of light piping has long been needed, no such solution in a multi-chambered cuvette having sufficient rigidity and optical properties to serve as a unitary disposable cartridge has heretofore appeared.
Other patents indicative of the state of the art are U.S. Pat. Nos. 3,520,659, 3,697,227, 3,532,470, 3,540,857, 3,582,283, 3,582,285, 3,545,934, 3,554,705, 3,477,821, 3,497,320, and 3,477,822.